Sensing of surgical instrument placement relative to anatomic structures

ABSTRACT

Systems and methods related to use of a measurement system in conjunction with a powered instrument for determination of the placement of a tool portion relative to the anatomy of a patient utilizing the powered instrument. The measurement system may include a displacement sensor that indicates the relative displacement of the tool portion relative to the anatomy. The system may also include a sensor for monitoring a tool drive signal representative of a tool drive parameter that is characteristic of the tool portion acting on the anatomy. The tool drive signal may be analyzed relative to a given amount of axial displacement as measured by the displacement sensor to avoid false indications of placement based on noise and or other artifacts in the tool drive signal that may result from characteristics of the anatomy and/or operational behaviors of the surgeon utilizing the instrument.

RELATED APPLICATIONS

This application is a National Stage Application under 37 CFR 371 of PCTApplication No. PCT/US2018/047847 filed on Aug. 24, 2018 entitled“SENSING OF SURGICAL INSTRUMENT PLACEMENT RELATIVE TO ANATOMICSTRUCTURES”, which claims the benefit of U.S. Application No. 62/550,423filed on Aug. 25, 2017 entitled “SENSING OF SURGICAL INSTRUMENTPLACEMENT RELATIVE TO ANATOMIC STRUCTURES”, the entirety of which isincorporated by reference herein.

BACKGROUND

The use of powered surgical instruments is common in many surgicalprocedures. Examples of such instruments may include drills, saws,grinders, or the like that may be electric, pneumatic, hydraulic, orotherwise powered. Often times, use of such powered surgical instrumentsmay allow for more efficient surgical operations, thus resulting inreduced risk to the patient, improved efficiency for the surgeon, andlower costs.

However, while such powered surgical instruments may provide advantagesover human powered instruments, there may also be increased risk forinadvertent damage to the anatomy of the patient when using poweredinstruments. For instance, surgical procedures often require preciseplacement of tools relative to the anatomy of a patient. In this regard,surgeons may, when using powered instruments, rely solely on the sensesof the surgeon to determine when a tool is in a certain positionrelative to the anatomy of a patient. For instance, when drillingthrough the bone of a patient, “plunge” may occur when the drill bitused with a drill may erupt from the distal portion of the bone throughwhich a bore is being drilled. A surgeon may be required to anticipateand/or react to plunge to cease operation of the drill to reduce thepotential for damage to tissue beyond the bone to be drilled.

However, the use of a surgeon's senses alone to “feel” when a tool in acertain position relative to the anatomy of a patient may have limits.For instance, repeatability may suffer as each patient may presentunique anatomy that presents to the surgeon in a different manner.Moreover, as the use of a surgeon's senses alone is highly subjective,certain placements may be more readily and repeatedly achieved by some,but possibly not all, surgeons. Further still, when utilizing poweredsurgical instruments, the ability for a surgeon to accurately use his orher senses to place a tool relative to the anatomy of a patient may becompromised as the surgical tool may mask or attenuate any availablefeedback provided to the surgeon when using such instruments. Furtherstill, events related to placement of tools may occur very rapidly, suchthat reaction times among various surgeons may differ or be too slow toaccurately control the operation of the tool. As such, the use ofpowered surgical instruments, while providing distinct advantages inmany operations, continue to suffer from drawbacks that limit thepotential benefits of such tools.

SUMMARY

In view of the foregoing, the present application relates to improvedsensing for the placement of a tool by a powered surgical instrumentrelative to the anatomy of a patient. Specifically, the presentdisclosure utilizes a measurement system in conjunction with a poweredsurgical instrument to determine the placement of the tool relative tothe anatomy of a patient. The measurement system may include orotherwise be in operative communication with a controller to analyzesensor outputs that relate to drive parameters of the tool. Thecontroller may be a computerized system (e.g., including a processor andmemory) capable of rapid analysis of the sensor outputs to controloperation of the instrument in response to the analysis of the sensoroutputs. Prior approaches to such measurement systems have beenproposed, such as in U.S. patent application Ser. No. 15/336,202 filedon Oct. 27, 2016 entitled “TECHNIQUES AND INSTRUMENTS FOR PLACEMENT OFORTHOPEDIC IMPLANTS RELATIVE TO BONE FEATURES,” the entirety of which isincorporated herein by reference in its entirety.

In such prior approaches to measurement systems for placement of toolsrelative to anatomical structures of a patient, a number of sensors thatproduce sensor outputs corresponding to characteristics of the tool wereutilized such that an analysis of the sensor outputs is used todetermine placement of the tool. However, in such systems, it may bedifficult to accurately determine placement relative to the anatomy fora number of reasons.

For instance, it has been found that the manner in which surgeons usepowered instruments may vary in relation to the rate and/or manner atwhich the instrument is advanced. In turn, the monitored parameters ofsuch systems used to determine instrument placement may be difficult toanalyze consistently. For instance, the force used to advance theinstrument, whether and the degree to which a surgeon retracts theinstrument between periods of advancement (e.g., “pecks”), and otherpotential variations in use may all may affect the characteristics orparameters monitored by a measurement system in determining theplacement of an instrument. It has been found that certain surgeonbehaviors may result in false indications of instrument placement.

Moreover, variations in anatomy may also lead to false indications ofplacement. For instance, different patients may have differentanatomical characteristics that are difficult to accurately model whenanalyzing sensor outputs in a traditional manner. Further still,anatomic structures may not provide sufficient uniformity for modelingusing the traditional approaches. As an example, it has been proposed tomonitor a force and a displacement signal to determine placement of atool relative to anatomical structures of a bone of a patient. In suchapproaches, a medullary layer of the bone has been modeled as auniformly dense region of the bone that is relatively less dense thanthe hard outer cortex of the bone. However, in reality trabeculae, whichare osseous fibers extending through the medullary may affect themeasured parameters or characteristics used to determine placement ofthe instrument.

In this regard, it may be appreciated that applications exist in whichthe analysis of sensor data may be difficult in view of any one of theforegoing examples. Namely, these scenarios may include noise in thesignals analyzed and/or low magnitude signals. For instance, noise maybe created in the signal due to anatomical structure (e.g.,trabeculations as described above), mechanical vibration of theinstrument as it operates, mechanical binding of the tool relative tothe anatomy of the patient, or the like. Furthermore, electricallyinduced noise, while preferably minimized by the design of theelectronic components of the instrument/controller, may still bepresent. In any regard, the result may include reduced signal to noiseratios that make accurately analyzing signal to detect instrumentplacement more difficult.

However, a number of approaches are described herein that may assist insuch signal analysis to improve accuracy of instrument placement even innoisy contexts with relatively low signal to noise ratios. Theapproaches described herein may be applied to any or all of the signalsanalyzed in the system. In a particular application, a tool driveparameter may be measured by a sensor to output a tool drive signal,upon which the approaches described herein may be used. Specifically,the tool drive parameter may be monitored for a change in the tool driveparameter (e.g., to detect an increase or decrease in force associatedwith the tool portion of an instrument passing from one medium toanother). Such a tool drive parameter may include, for example, an axialforce acting on the tool, a torque acting on the tool, or an electricalcharacteristic of a drive motor of the powered surgical instrument(e.g., a resistance, power, load, or other measure of the drive motor).Appropriate sensors may be provided for measuring or monitoring any ofthe foregoing tool drive parameters and outputting the tool driveparameter including force sensors, torque sensors, or other measurementsensors.

The approaches described herein may all act to identify a change in thetool drive parameter over a given amount of axial displacement of thetool portion. The change in the tool drive parameter may be indicativeof a tool portion of the instrument acting on a different medium ofanatomy (e.g., passing from one layer of a bone to another). In thisregard, the change in the tool drive parameter may be measured relativeto the given amount of axial displacement. Specifically, changes in thetool drive parameter that are not sustained over the given amount ofaxial displacement may not be identified by the controller as actuallycorresponding to the tool portion passing from one medium to another.Such changes in the tool drive parameter occurring over distances lessthan the given amount of axial displacement may be the result of noise,operator behavior, or anatomical structures (e.g., trabeculations). Inany regard, such changes in the tool drive parameter occurring overdistances less than the given amount of axial displacement arepreferably disregarded to avoid false detection of placement of the toolportion. In this regard, approaches described herein may analyze a tooldrive parameter in relation to axial displacement rather than relativeto time. Accordingly, any such analysis to determine a change in a tooldrive parameter may be conducted without respect to time. Such anapproach may include collecting tool drive parameter data for eachincrement of axial displacement that is greater than a previous value.That is, if the tool portion is retracted and readvanced, any datacollected during the readvancement of the tool portion may bedisregarded such that only the first instance of axial displacementincludes tool drive parameter data collection.

A first approach to analysis of the signal may include filtering thesignal such that variation within the signal that occurs in an axialdisplacement less than the given amount of axial displacement areremoved from the signal. In this regard, a low pass filter may beprovided that removes portions of the signal at relatively highfrequencies. The filter may be implemented in hardware or software.Moreover, a cutoff frequency of the filter may be tuned in view of thegiven amount of axial displacement or other displacement signal.

Another approach described herein relates to determining an integralvalue of the tool drive parameter. This may include summing the tooldrive parameter over a plurality of instances of the given amount ofaxial displacement. As may be appreciated, the tool drive parametersignal may be plotted relative to the axial displacement of the toolportion. In turn, the integral of the signal relative to the axialdisplacement may provide the area under the curve plotted and representa summation of the signal over a given distance. This integral value ofthe tool drive parameter may be referred to as an integrated tool driveparameter representative of a summation of the drive parameter over aplurality of increments of axial displacement. In turn, an integralthreshold value may be established such that the change in the tooldrive parameter is identified when the integrated tool drive parameterexceeds the integral threshold. In the event that the integrated tooldrive parameter for any given integral window over which the tool driveparameter is summed is less than the integral threshold, no change maybe detected in the given integral window. This may be despite localincreases or decreases in the tool drive parameter over the integralwindow. However, once an integral window includes an integrated tooldrive parameter exceeds the integral threshold, the change in the tooldrive signal may be identified in accordance with any applicable toolplacement modality active at the instrument.

Still another approach includes calculation of a moving average of thetool drive parameter. This may act to smooth the tool drive parameter.The moving average may be calculated over the given amount of axialdisplacement such that spikes in the tool drive parameter that occurover a very short axial displacement (e.g., noise) may not significantlyalter the moving average of the tool drive parameter. In turn, themoving average may be analyzed to determine a change in the movingaverage that is indicative of the tool portion moving from a firstmedium to a second medium. As will be described in greater detail below,this may include monitoring for an inflection point in the movingaverage that may indicate the tool portion moving from a harder materialto a softer material or from a softer material to a harder material.

In another approach related to moving averages of the tool driveparameter, a first and second moving average may be determined. One ofthe moving averages may be a relatively short term moving averagecalculated with fewer values of the tool drive parameter reflectingchanges over a shorter axial displacement. In contrast, the other movingaverage may be a relatively long term moving average calculated withmore vales of the tool drive parameter over a greater distance of axialdisplacement. In turn, a change of the first signal relative to thesecond signal may be identified that may indicate the tool portionmoving from a first to a second medium. As will be appreciated in thediscussion to follow, any of the foregoing approaches may be used,potentially in combination, and potentially with other analysistechniques to assist in identifying placement of a tool portion.

Accordingly, a first aspect of the present disclosure includes ameasurement system for use with a powered surgical instrument forsensing a position of a leading edge of a tool relative to anatomicstructures of a patient. The measurement system includes a first sensordisposed with respect to the powered surgical instrument to measure atool drive parameter that is characteristic of the tool portion actingon the patient. The first sensor also outputs a tool drive signalrepresentative the tool drive parameter as the tool is advanced relativeto anatomy of the patient. The measurement system also includes adisplacement sensor disposed with respect to the powered surgicalinstrument to measure an axial displacement of the leading edge of thetool relative to a reference point. The displacement sensor also outputsa displacement signal representative of the axial displacement. Themeasurement system further includes a controller in operativecommunication with the first sensor to receive the tool drive signal andin operative communication with the displacement sensor to receive thedisplacement signal. The controller is operative to identify a change inthe tool drive parameter over a given amount of axial displacement ofthe leading edge of the tool that is indicative of the leading edge ofthe tool moving through an interface between anatomic structures of thepatient.

A number of feature refinements and additional features are applicableto the first aspect. These feature refinements and additional featuresmay be used individually or in any combination. As such, each of thefollowing features that will be discussed may be, but are not requiredto be, used with any other feature or combination of features of thefirst aspect.

In an embodiment, the given amount of axial displacement of the leadingedge of the tool may be at least about 0.5 mm. In other embodiments, thegiven amount of axial displacement may be at least about 1.0 mm, 1.5 mm,2.0 mm, 2.5 mm, or even 3.0 mm.

When it is determined that the tool portion is placed relative to theanatomy of interested (which may be determined based on a mode selectionof the instrument), a number of actions may be performed by thecontroller. For instance, the controller may be in control of theoperation of a drive motor of the powered surgical instrument and may beoperative to stop the drive motor in response to identifying theinterface between anatomic structures of the patient. Additionally oralternatively, the controller may output a visual, auditory, or othertype of alert and/or record a measurement of the displacement of thetool portion at the identified position.

In various embodiments, the first sensor may correspond to one or moresensors for measuring a tool drive parameter. The tool drive parametermay include one of an axial force acting on the tool, a torque acting onthe tool, or an electrical characteristic of a drive motor of thepowered surgical instrument (e.g., a resistance, power, load, or othermeasure of the drive motor). Appropriate sensors may be provided formeasuring or monitoring any of the foregoing tool drive parametersincluding force sensors, torque sensors, or other measurement sensors.

For example, the anatomic structures of the patient have differentdensities. Accordingly, the change in the tool drive parameter maycorrespond to the working portion of the instrument passing from oneanatomical structure (e.g., a first medium) to another anatomicalstructure (e.g., a second medium). As the working tool begins to operatein the different anatomical structure with a different density, the tooldrive parameter may also change, which may be detected.

In a first approach, the controller may be operative to filter the tooldrive signal relative to the given mount of axial displacement of theleading edge of the tool portion. Accordingly, changes in the tool driveparameter over distances less than the given amount of axialdisplacement are not identified as indicative of the leading edge of thetool portion moving through the interface between anatomic structures ofthe patient. The controller may comprise a filter embodied in eitherhardware or software for these purposes as will be described in greaterdetail below.

In another approach, the controller may be operative to determine amoving average for the tool drive parameter with respect to the axialdisplacement of the leading edge of the tool portion relative to theanatomy of the patient. The controller may be operative to identify thechange in the tool drive parameter relative to a given amount of axialdisplacement of the leading edge of the tool portion based on aninflection of the moving average.

For instance, the interface may be from a medullary layer of a bone to acortex layer of the bone. As such, the moving average may include aninflection from a minimum of the moving average over the given amount ofaxial displacement of the leading edge of the tool. Alternatively, theinterface may be from a cortex layer of a bone to an exterior of thebone. In this case, the moving average may include an inflection from amaximum of the moving average over the given amount of axialdisplacement of the leading edge of the tool.

In another embodiment, the interface through which the leading edge ofthe tool moves may be from a medullary layer of a bone to a cortex layerof the bone. In this embodiment, one approach to detecting a change inthe tool drive parameter may include the controller operating todetermine an integrated tool drive parameter comprising a sum of thetool drive parameter over a given plurality of instances of the givenamount of axial displacement of the leading edge of the tool portion.The controller may be operative to compare the integrated tool driveparameter to an integral threshold value and identify the change in thetool drive parameter when the integrated tool drive parameter exceedsthe integral threshold value. The given plurality of instances of thegiven amount of axial displacement of the leading edge of the toolportion may comprise the immediately preceding instances of the givenamount of axial displacement to a current position of the leading edgeof the tool portion. In an example of this approach, the given amount ofaxial displacement may comprise 0.1 mm and the given plurality ofinstances may comprise ten instances.

In another approach, the controller may be operative to generate a shortterm moving average for the tool drive parameter with respect to a firstaxial displacement of the leading edge of the tool portion relative tothe anatomy of the patient and generate a long term moving average forthe tool drive parameter with respect to a second axial displacement ofthe leading edge of the tool portion relative to the anatomy of thepatient. The second axial displacement may be greater than the firstaxial displacement. In turn, the controller may identify the change inthe tool drive parameter when the short term moving average divergesfrom the long term moving average by at least a differential threshold.In this approach the controller may be operative to monitor for thechange in the tool drive parameter when the leading edge of the toolportion decelerates in three consecutive instances of the given amountof axial displacement of the leading edge of the tool portion. This mayinclude monitoring an average acceleration over three consecutiveintervals (e.g., with respect to time or axial displacement) todetermine whether, on average the tool is decelerating over theintervals. The controller may also be operative to determine thedeceleration in the leading edge based on the displacement signal bycalculating the second derivative of the displacement signal.

A second aspect includes a method for use with a powered surgicalinstrument for sensing a position of a leading edge of a tool relativeto anatomic structures of a patient. The method includes measuring atool drive parameter that is characteristic of the tool portion actingon the patient as the tool is advanced relative to anatomical structuresof the patient at a first sensor of the powered surgical instrument andoutputting a tool drive signal representative of the tool driveparameter. The method includes measuring at a displacement sensor of thepowered surgical instrument an axial displacement of the leading edge ofthe tool relative to a reference point and outputting a displacementsignal representative of the axial displacement. The method alsoincludes monitoring the tool drive signal and the displacement signal asthe leading edge of the tool is advanced relative to the anatomicalstructures of the patient. In turn, the method includes identifying achange in the tool drive parameter over a given amount of axialdisplacement of the leading edge of the tool that is indicative of theleading edge of the tool moving through an interface between anatomicstructures of the patient.

A number of feature refinements and additional features are applicableto the second aspect. These feature refinements and additional featuresmay be used individually or in any combination. As such, each of thefollowing features that will be discussed may be, but are not requiredto be, used with any other feature or combination of features of thesecond aspect.

For instance, in an embodiment, the method may include filtering thetool drive signal relative to the given amount of axial displacement ofthe leading edge of the tool such that changes in the tool driveparameter over distances less than the given amount of axialdisplacement are not identified as indicative of the leading edge of thetool moving through the interface between anatomic structures of thepatient. Additionally or alternatively, the method may includedetermining a moving average of the tool drive parameter with respect tothe axial displacement of the leading edge of the tool relative to theanatomical structures of the patient. In this latter regard, theidentifying may include identifying an inflection in the moving average.In this regard and as described above, the interface may be from amedullary layer of a bone to a cortex layer of the bone, and the movingaverage may include a corresponding inflection from a minimum of themoving average over the given amount of axial displacement of theleading edge of the tool. Alternatively, the interface may be from acortex layer of a bone to an exterior of the bone, and the movingaverage may include a corresponding inflection from a maximum of themoving average over the given amount of axial displacement of theleading edge of the tool.

In an embodiment, upon identifying the change in the tool driveparameter that indicates placement of the tool portion in a desiredlocation, a number of actions may be taken (e.g., by the controller ofthe instrument). For instance, the method may include stopping operationof a drive motor of the powered surgical instrument in response to theidentifying. Additionally or alternatively, the method may includealerting a user and/or measuring a displacement associated with theplacement of the tool portion.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an embodiment of an instrument having ameasurement system with a front wall of a housing not shown to provideillustration of various components within the housing.

FIGS. 2 and 3 are side cut-away views of the instrument shown in FIG. 1taken down a center portion of the instrument.

FIG. 4 is a perspective view of an embodiment of a chuck engagementportion of an instrument with a portion of the instrument housing hiddento provide illustration of the chuck engagement portion.

FIG. 5 is a perspective view of an embodiment of a chuck.

FIG. 6 is a schematic representation of bicortical placement of a toolportion relative to a bone of a patient.

FIG. 7 is a schematic representation of subchondral placement of a toolportion relative to a bone of a patient.

FIG. 8 is a schematic representation of endosteal placement of a toolportion relative to a bone of a patient.

FIG. 9 is a schematic representation of multicortical placement of atool portion relative to a bone of a patient.

FIG. 10A depicts an embodiment of an interface of a controller.

FIG. 10B depicts an embodiment of an instrument interface of thecontroller of FIG. 10A.

FIGS. 11 and 12 depict plots representing an embodiment of operation ofthe instrument.

FIG. 13 depicts a plot representing an embodiment of operation of theinstrument in relation to a schematic view of the anatomy through whicha tool portion is advanced.

FIG. 14 is a flowchart of an embodiment of a method for operation of aninstrument.

FIG. 15 is a flowchart of an embodiment of an approach to detection of achange in a tool drive parameter.

FIG. 16 is a plot depicting the tool drive parameter and analysisaccording to the embodiment of the approach depicted in FIG. 15.

FIG. 17 is a flowchart of an embodiment of an approach to detection of achange in a tool drive parameter.

FIG. 18 is a plot depicting the tool drive parameter and analysisaccording to the embodiment of the approach depicted in FIG. 17.

DETAILED DESCRIPTION

The following description is not intended to limit the invention to theforms disclosed herein. Consequently, variations and modificationscommensurate with the following teachings, skill and knowledge of therelevant art, are within the scope of the present invention. Theembodiments described herein are further intended to explain modes knownof practicing the invention and to enable others skilled in the art toutilize the invention in such, or other embodiments and with variousmodifications required by the particular applications(s) or use(s) ofthe present invention.

As described above, the present disclosure includes details that relatesto the use of a powered surgical instrument having a measurement systemfor determining the placement of a tool portion of the powered surgicalinstrument relative to anatomy (e.g., a bone) of a patient. Forinstance, in various embodiments the tool portion may comprise a drillbit, a saw blade, a grinding tool, or other tool portion used forsurgical operations. In other embodiments, the tool portion may includea pin or wire that is placed in the bone of the patient using a poweredinstrument such as a drill or the like. FIGS. 1-3 depict an embodimentof a powered surgical instrument 10 that may be utilized for suchplacement of a tool portion 62. As used herein, the powered surgicalinstrument 10 may alternatively be referred to as the powered instrument10 and/or the instrument 10. Moreover, the tool portion 62 may bealternatively referred to as the tool 62.

As may be appreciated, tool portions 62 used in conjunction with apowered surgical instrument 10 may be used in a wide variety of surgicalapplications. For instance, drill bits may be used to bore holes in theanatomy of a patient, including bones. Furthermore, saws or grinders mayalso be utilized in orthopedic or other types of procedures. Furtherstill, the use of implants such as pins (e.g., IM pins) and/or wires(e.g., K-wires) may be used in a variety of surgical applications,especially in the field of orthopedic surgery. The implants may be usedto provide traction to the bones of a patient. Moreover, the implant maybe placed to allow for induced motion of a bone (e.g., to providealignment, rotation, or other manipulation of a bone). Furthermore,orthopedic implants may be used for fixation to secure fractured boneportions. In any regard, for the various embodiments and contexts ofuses for the tool portions 62 contemplated herein, different relativeplacements may be desired. Such placement may be aided when using apowered surgical instrument 10 by use of a measurement system 40 thatmay assist in determining placement of the tool portion 62 as describedin detail below.

As will be described in greater detail below, use of a poweredinstrument 10 having a measurement system 40 may provide a number ofbenefits in relation to placement of a tool portion 62. For instance,because the measurement system 40 may have the capability ofautomatically detecting when a tool 62 passes through a particularportion of anatomy, the user of the instrument may not be required todetermine placement of the tool 62 by “feel” alone. In turn, the timerequired to place a tool 62 may be reduced. Moreover, the repeatabilityand/or reliability of tool 62 placement may be increased. Specifically,the present disclosure relates to improved systems and methods thatallow for more accurate reliable tool 62 placement. Such reliability maybe provided by various filtering and/or signal processing approachestaken by a computerized controller of the measurement system 40 thatwill be described in greater detail below.

The instrument 10 may include a chuck 20 for engagement of the toolportion 62. The tool portion 62 may comprise a tool assembly 60 that maybe specifically adapted for utilization with the measurement system 40of the instrument 10. For instance, the assembly 60 may include the toolportion 62 and a correspondingly sized bushing 64 as will be describedin greater detail below.

A drive system 30 may be provided that may include a motor 32. In atleast some embodiments, the drive system 30 may also include a gearbox34. In turn, the drive system 30 may engage the chuck 20 to impartrotational motion to the chuck 20 about a working axis 16. In otherembodiments, vibratory or oscillating motions (e.g., in the case of asaw or the like) may be created such that a tool engagement portionimparts an appropriate movement to the tool portion 62. In suchcontexts, the working axis 16 may be an axis along which the toolportion 62 is advanced, where the motion of the tool may be along ororthogonal to the working axis 16. In embodiments in which the motionimparted by the drive system 30 is rotary, the working axis 16 maydefine an axis of rotation about which the drive system 30 may inducerotation of the chuck 20 and, when engaged therewith, a tool portion 62.

In any regard, the tool portion 62 may be advanced along the workingaxis 16.

Notably, the chuck 20 and drive system 30 may be cannulated to accept atool portion 62 corresponding to a pin or wire as described above.Furthermore, the drill housing 12 may also be cannulated such that atool portion 62 may pass entirely through the body the instrument 10including the chuck 20, drive system 30, and housing 12. In this regard,the instrument 10 may include a cannulated passage 76 that may extendfrom the proximal portion of the instrument 10 to a distal portionthereof. This cannulated passage may be defined, at least in part, bythe chuck 20, the drive system 30, and/or the housing 12. As such, thechuck 20 may also include a cannulated passage 22. In this regard and aswill be described in greater detail below, the cannulated passage 22 ofthe chuck 20 may be selectively aligned to the cannulated passage 76 ofthe instrument 10 in embodiments where the chuck 20 selectivelyremovable from the instrument 10 for interchanging of the chuck utilizedwith the instrument 10.

With continued reference to FIGS. 1-3, an embodiment of a measurementsystem 40 is shown. The instrument 10 may be adapted for use with a toolassembly 60 that may include a bushing 64. The bushing 64 may becorrespondingly sized to extend about at least a portion of the toolportion 62 to allow for constrained axial movement of the bushing 64relative to the tool portion 62. Alternatively, the bushing 64 may beintegrally provided with the measurement system 40 as described ingreater detail below. The instrument 10 may comprise at least somecomponents of the measurement system 40 within the housing 12 tofacilitate operation of the measurement system 40 in connection with theinstrument 10. For example, at least a portion of a displacement sensor42 may be integrated into a housing 12 of the instrument 10. In thisregard, the displacement sensor 42 may include a depth sensing arm 44that is specifically adapted for engagement with the bushing 64 of thetool assembly 60 that may be engaged by a chuck 20 or other engagementportion of the instrument 10. While the bushing 64 is shown as adiscrete part, the bushing 64 may also be provided integrally with thedisplacement sensing arm 44.

The measurement system 40 may also include a force sensor 50. The forcesensor 50 may be disposed relative to the drive system 30. The chuck 20and drive system 30 may contact the force sensor 50 such that the forcesensor 50 is capable of measuring an axial force acting on the toolportion 62 along the working axis 16. In this regard, the chuck 20 anddrive system 30 may be axially rigid such that an axial force acting onthe chuck 20 (e.g., as imparted to the implant 62 upon axial advancementof the tool portion 62 engaged with the chuck 20) may be passed to thechuck 20 and drive system 30 such that the drive system 30 may impingeon the force sensor 50 such that the force sensor 50 may measure theforce. Thus, the chuck 20 and drive system 30 may be supported such thatthe axial movement of the chuck 20 and drive system 30 is limited (e.g.,to prevent error in relation to the displacement sensor 42) yet allowfor the free transfer of force to the force sensor 50. That is, it isadvantageous to reduce the action of errant forces on the chuck 20 anddrive system 30 along the working axis 16 to improve the accuracy of themeasured force at the force sensor 50. For instance, upon contact of thedrive system 30 with the force sensor 50, further axial forces on thedrive system 30 may result in minimal deflection (i.e., imperceptibly bythe displacement sensor 40) while impinging on the force sensor 50. Inthis regard, the drive system 30 may be constrained for contactingengagement with the force sensor 50, but otherwise free to deflect alongthe working axis to achieve an accurate force measurement. In at leastsome embodiments, the drive system 30 may be preloaded to impart apreloaded force against the force sensor 50. In this regard, the forcesensor 50 may measure a differential between the preload force and ameasured force to determine an applied force to the tool portion 62.

The drive system 30, displacement sensor 42, and/or force sensor 50 mayeach be in operative communication with a controller 146. The controller146 may be a computerized controller that may include a processor andmemory that stores instructions executable by the processor to performsignal analysis of the outputs of the displacement sensor 42 and/orforce sensor 50. Furthermore, the controller 146 may be in control ofthe drive system 30 (e.g., to control the operation and/or cessation ofoperation of the drive system 30). As shown in FIGS. 10A and 10B, thecontroller 146 may comprise a remote unit to which the instrument isoperatively coupled for communication therewith. Alternatively, thecontroller 146 may be integrated into the housing 12 of the instrument10. The operation of the controller 146 in relation to the instrument 10is described in greater detail below.

Returning to the description of the displacement sensor 42, the depthsensing arm 44 may be used to establish a reference point from whichdisplacement of a tool portion 62 may be measured. In this regard, asfollows herein, a general description of the features and operation ofthe instrument 10 used in conjunction with the tool assembly 60 isprovided.

The depth sensing arm 44 may extend from the drill housing 12. Forexample, the depth sensing arm 44 may extend distally (e.g., from adistal face 14 of the drill housing 12) in a direction correspondingwith the direction in which the tool portion 62 extends from the chuck20 of the instrument 10 for advancement relative to the anatomy of thepatient. At least a portion of the displacement sensing arm 44 mayextend from the drill housing 12 parallel to the working axis 16 of theinstrument 10. The depth sensing arm 44 may also include a distalportion 46 that is adapted to engage the bushing 64 provided with thetool assembly 60. Alternatively, the distal portion 46 may include anintegrally provided bushing 64 as described above. As used herein,distal may correspond to a direction toward the leading edge 10 a of thetool portion 62 and proximal may correspond to a direction away from theleading edge 10 a of the tool portion 62 toward an opposite end of thetool portion 62. In this regard, at least a portion of the depth sensingarm 44 (e.g., the distal portion 46) may be adapted to engage thebushing 64 of the tool assembly 60. In any regard, at least a portion ofthe depth sensing arm 44 may extend into the housing 12.

In an embodiment, the displacement sensor 40 may comprise a linearvariable differential transformer (LVDT) sensor that is adapted to sensethe position of a core 54 relative to a coil 48. Accordingly, thehousing 12 may contain a coil 48. A proximal end 52 of the displacementsensing arm 44 may include the core 54 that may interact with the coil48 of the displacement sensor 40. Specifically, as shown in FIG. 1, thedepth sensing arm 44 is in a retracted position relative to the toolportion 62. For example, this retracted position shown in FIG. 1 mayoccur when the tool portion 62 is advanced during placement of the toolportion 62 relative to the anatomy of a patient (e.g., such that theportion of the tool portion 62 extending beyond the distal edge of thebushing 64 would be disposed in the anatomy of the patient such as abone or the like). In this regard, the proximal end 52 of thedisplacement sensing arm 44 may be disposed within the coil 48 of thedisplacement sensor 40. Accordingly, as the proximal end 52 of thedisplacement sensing arm 44 is moved relative to the coil 48, thelocation of the core 54 may be determined relative to the coil 48 (e.g.,by monitoring the induced current of the coil 48) to provide an outputthat is indicative of the position of the core 54, and in turn theposition of the displacement sensing arm 44 relative to the drillhousing 12. That is, the depth sensing arm 44 may be displaceablerelative to the coil 48 such that the displacement sensor 42 may beoperable to sense a change in position of the depth sensing arm 44 andoutput a measure of the displacement that may be used in determining adepth of penetration of the tool portion 62 relative to the anatomy thetool portion 62 is advanced. In an embodiment, the total measurabletravel of the core 54 relative to the coil 48 may be at least about 2.5in (6.4 cm). Furthermore, the resolution of the output of thedisplacement sensor 42 may be about 0.1% (e.g., about 0.002 inches (0.06mm) for a sensor having a total measurable travel of 2.5 inches (6.4cm)).

While a LVDT displacement sensor is shown and described in relation tothe instrument 10 shown in the accompanying figures, it may beappreciated that other types of displacement sensors may be provided.For instance, the sensor may provide for the absolute or relativemeasurement of the position of the distal end 46 of the displacementsensing arm 44 to provide a displacement measure. For instance, inanother embodiment, an optical displacement sensor may be provided.Other types of displacement sensors are also contemplated such as, forexample, a capacitive displacement sensor, ultrasonic sensors, Halleffect sensors, rotary encoders, linear encoders, or any other sensorsknown in the art capable of outputting an absolute or relative positionmeasure. In any regard, the use of the bushing 64 that is engaged withthe displacement sensing arm 44 may allow for a reference point to beestablished using the bushing 64 resting external to the substrate intowhich the tool portion 62 is advanced. For instance, the controller 146may receive an input to reset or “zero” the measure of the displacementsensor 42 when the bushing and leading edge 10 a of the tool portion 62are in contact with a reference (e.g., an exterior portion of a bone)into which the tool portion 62 is to be advanced. Accordingly, anyrelative movement of the tool portion 62 relative to the bushing 64 maybe measured by the controller 146 to determine the depth of penetrationof the leading edge 10 a of the tool portion 62 as it is advanced intothe anatomy of the patient (e.g., a patient's bone).

A biasing member 58 (e.g., a coil spring) may be provided relative tothe proximal end 52 of the displacement sensing arm 44. In this regard,the biasing member 58 may act on the proximal end 52 of the displacementsensing arm 44 to bias the displacement sensing arm 44 distally. Thismay assist in maintaining the bushing 64 in contact with the bone toincrease the accuracy of the displacement sensor 42.

In an embodiment, the displacement sensing arm 44 may include featuresthat selectively prevent ejection of the displacement sensing arm 44from the instrument in the distal direction when the displacementsensing arm 44 is distally biased. For example, the displacement sensingarm 44 may include at least one flat portion 66 that extends along aportion of the displacement sensing arm 44. At the proximal and distalextents of the flat 66, the displacement sensing arm 44 may includeshoulders 68 that project from the flat 66. As such, a selectivelydisplaceable stop 70 (best seen in FIGS. 2 and 3) may be disposedrelative to the flat portion 66 such that the flat portion 66 may movedistally and proximally relative to the stop 70. However, the stop 70may interfere with the shoulder 68 defined in the displacement sensingarm 44 to prevent passage of the shoulders 68 beyond the stop 70. Thatis, a distal shoulder 68 may limit proximal movement of the displacementsensing arm 44 beyond the stop and a proximal shoulder 68 may limitdistal movement of the displacement sensing arm 44 beyond the stop 70.In this regard, the length of the displacement sensing arm 44 alongwhich the flat portion 66 extends may be moveable relative to the stop70 between the distal and proximal shoulders 68 defined at the ends ofthe flat portion 66.

However, the stop 70 may be displaceable by, for example, depressing abutton 72 provided on an exterior of the housing 12. Thus, upondepressing the button 72, the stop 70 may be displaced away from thedisplacement sensing arm 44 to allow the shoulder 68 to pass by the stop70 such that the displacement sensing arm 44 may be removed from theinstrument 10. Additionally, the distal end of the flat 66 may include adetent 74 that may be engageable with the stop 70 so as to maintain thedisplacement sensing arm 44 in a proximally disposed, retracted positionrelative to the housing 12 such as that shown in FIG. 1. Once the button70 is depressed and released, the detent 74 at the proximal end of theflat portion 66 may be released by the stop 70 and the displacementsensing arm 44 may move proximally (e.g., under influence of the biasingmember 58). The displacement sensing arm 44 may move proximally untilthe shoulder 68 at the distal end of the flat 66 are engaged to preventfurther distal movement of the displacement sensing arm 44. Accordingly,the displacement sensing arm 44 may be retained in a retracted position(e.g., for improved visibility of the distal end of the tool portion 62or to stow the displacement sensing arm 44 when not in use). However,the displacement sensing arm 44 may be released to be moveable relativeto the housing 12. Moreover, the displacement sensing arm 44 may beremovable altogether from the housing 12.

In the latter regard, removal of the displacement sensing arm 44 andbiasing member 58 from the instrument 10 may allow for separate cleaning(e.g., in an autoclave) of those members. Additionally, removal of thedisplacement sensing arm 44 may allow for a cleaning apparatus (e.g., abrush or the like) to be passed through the instrument 10 to facilitatecleaning thereof.

As referenced above, in an embodiment the distal portion 46 of thedisplacement sensing arm 44 may be adapted to engage the tool assembly60 (e.g., a bushing 64 thereof) that is correspondingly adapted for usewith the instrument 10. In this regard, the tool assembly 60 may includethe tool portion 62 and the bushing 64. The bushing 64 may be adaptedfor movement along the tool portion 62 relative to the working axis ofthe tool portion 62. The displacement sensing arm 44 may engage thebushing 64 such that movement of the bushing 64 relative to the toolportion 62 may also cause relative movement of the displacement sensingarm 44 relative to the tool portion 62. The displacement sensing arm 44may generally be linear along a proximal portion 52 of the displacementsensing arm 44. In this regard, the proximal portion 52 may be adaptedto be parallel with the cannulated passage 76 that extends along theworking axis 16.

Furthermore, the distal portion 46 of the displacement sensing arm 44(e.g., the portion distal to the linear portion of the displacementsensing arm 44) may extend from the linear portion of the displacementsensing arm 44 toward the tool assembly 60 that may be engaged by thechuck 20 of the instrument 10. In this regard, the linear portion of thedisplacement sensing arm 44 may be substantially parallel to and offsetfrom the working axis 16. The distal portion 46 may extend from thelinear portion in a direction corresponding with the offset such thatthe distal portion 46 extends toward the tool assembly 60. This mayfacilitate engagement between the displacement sensing arm 44 and thebushing 64 of the tool assembly 60 (e.g., using a post and hole asdescribed in U.S. Pat. No. 9,370,372, which is incorporated by referenceherein in its entirety).

The distal portion 46 may be an at least partially arcuate memberextending along a radius of curvature toward the tool assembly 60.However, the distal portion 46 may be shaped differently (e.g., thedistal portion 46 may be a linear portion extending at an angle orperpendicularly from the proximal portion 52 toward the tool assembly60). The configuration and operation of the measurement system 40 of theinstrument 10 may be as described in any of the embodiments in U.S. Pat.Nos. 6,665,948, 9,370,372, or U.S. Patent Pub. No. 2016/0128704, all ofwhich are incorporate by reference herein in their entireties. Moreover,operation of the bushing 64 in relation to the displacement sensing arm44 may be according to any of the foregoing documents incorporated byreference. In this regard, the bushing 64 may interact with the toolportion 62 in a manner similar to that described in relation to thebushing interacting with the drill bit or other instrument tool portion62 described in the foregoing documents incorporate by reference.

As described briefly above, the chuck 20 may be selectively engageableand disengageable with the instrument 10. In this regard, variousdifferent chucks may be selectively utilized in conjunction with theinstrument 10. To facilitate the different chucks, the instrument 10 mayprovide a standardized chuck engagement format to engage the variousdifferent potential embodiments of chucks 20 that may be utilized withthe instrument 10. In this regard, as may be appreciated in FIG. 4, theinstrument 10 may include a corresponding chuck drive coupling 78 thatengages with a chuck 20 to impart rotational motion from the drivesystem 30 to the chuck 20. In this regard, the chuck 20 may bedetachable from the drill 50. The chuck drive coupling 78 may be inoperative communication with the drive system 30 such that the drivesystem 30 rotates the drive coupling 78. In turn, the chuck drivecoupling 78 may engage with the chuck 20 to rotate at least a portionthereof. Furthermore, any chuck 20 configured for engagement with theinstrument 10 may include a cannulated passage 22 that is alignable withthe cannulated passage 76 of the instrument when the chuck 20 is engagedtherewith.

With further reference to FIG. 5, the proximal end of the chuck 20 mayinclude a chuck drive shaft 24 disposed relative to slots 26. The slots26 may coordinate with corresponding tabs 80 provided with theinstrument 10 adjacent to the chuck drive coupling 78 (best seen inFIGS. 2 and 3) to retain the chuck 20 relative to the instrument 10. Forinstance, the tabs 80 may be rigidly engaged with the drive system 30.In turn, the chuck drive shaft 24 may be keyed or otherwise configuredsuch that the chuck shaft 24 engages the chuck drive coupling 78 of theinstrument 10. In turn, the chuck drive coupling 78 may impartrotational motion to the chuck drive shaft 24 to rotate a tool portion62 engaged with the chuck 20. The slots 26 may coordinate with the tabs80 so as to allow the chuck 20 to be quickly attached and/or releasedfrom the instrument 10 by engagement of the slots 26 with the tabs 80.This may be appreciated from FIG. 5, where it is illustrated that theslots 26 may include a first portion 26 a that extends parallel to theworking axis 16.

The chuck may be advanced toward the chuck drive coupling 78 along theworking axis 16 such that the tabs 80 travel along the first portion 26a to the distal end thereof. The slots 26 may also include a secondportion 26 b that extend circumferentially about the chuck 20. As such,once the tabs 80 abut the distal end of the first portion 26 a, rotationof the chuck 20 may move the second portion 26 b such that the tabs 80extend into the second portion 26 b, thus restricting the chuck 20 frommovement relative to the working axis 16. That is, when the tabs 80 aredisposed in the second portion 26 b, the second portion 26 b may besized as to engage the tabs 80 to limit axial movement of the chuck 20relative to the working axis 16 (e.g., to allow the chuck 20 to travelrelative to the force sensor 50 for transferring force thereto, but todisallow the chuck 20 from moving distally from the instrument 10).Further locking mechanisms may be provided to prevent the chuck 20 fromrotating relative to the working axis 16 when engaged so that the tabs80 do not slip from the second portion 26 b. For example, a release maybe provided to lockingly maintain the chuck 20 in position to theinstrument 10 such that the chuck 20 is only released for removal uponactuation of the release. Thus, the chuck 20 may be quickly andefficiently attached and detached from the instrument 10.

In this regard, when the chuck 20 is engaged with the drive system 30,the tool portion 62, chuck 20, and drive system 30 may define an axiallyrigid structure that may transmit a force acting axially on the toolportion 62 along the working axis 16 along the rigid structure such thatthe force sensor 50 is operative to detect the force acting on the toolportion 62. As is discussed in greater detail below, a controller of theinstrument 10 may be operative to monitor one or more parameters of theinstrument 10 to determine placement of the tool portion 62.

With further reference to FIGS. 10A and 10B, an embodiment of acontroller 146 is shown that may be utilized with the instrument 10.Specifically, as described above, the instrument 10 may have adisplacement sensor 42 for outputting a signal indicative of therelative displacement of a tool portion 62 (e.g., a leading edge 10 a ofthe tool portion 62). Also, the instrument 10 may have a force sensor 50for measurement of the force acting on the tool portion 62 axially alongthe working axis 16. In other embodiments, additional or alternativesensors may be provided for generating tool drive signals representativeof a tool drive parameter that is characteristic of the operation of thetool portion 62. The instrument 10 may include a telemetry cable 174 inoperative communication with the displacement sensor 42 and the forcesensor 50. The telemetry cable 174 may have a connector 172 that mayinterface with a data port 170 of the controller 146. While a telemetrycable 174 is shown for interfacing with the controller 146, otherapproaches are possible for relay of data from the instrument 10 to acontroller 146 such as, for example, by way of wireless telemetry via awireless protocol such as Bluetooth, IEEE 802.11, or the like.Furthermore, the controller 146 may not be a separate unit, but may beintegrated into the instrument 10 as described above.

As depicted, the controller 146 may include a touchscreen interface 152for use by a user to interface with the controller 146. The interface146 may allow a user to set a diameter or other characteristic of theworking tool 62 at a selection portion 160. Moreover, the rotationalspeed of the instrument may be displayed and/or controlled at the speedselection 162. An operation mode may be selected or input at the modeselection 150 as will be described in greater detail below. Also, theinstrument direction may be selected or input at the direction selection164. In an embodiment, the instrument 10 may measure a depth of a bore.This may be output in the length measurement output 166. Also, thecontroller 146 may have a reset selection 153 to allow for resetting theinstrument (e.g., for establishing a reference point for thedisplacement sensor 42 and/or calibrating the force sensor 50). While areset selection 153 may be provided on the controller 146, the resetselection 153 may be triggered by use of a first trigger 90 and a secondtrigger 92 of the instrument 10. For instance, in normal operation,actuation of the first trigger 90 may result in operation of theinstrument 10 in a first direction (e.g., clockwise relative to theworking axis 16). Actuation of the second trigger 92 may result inoperation of the instrument 10 in an opposite direction (e.g.,anticlockwise relative to the working axis 16). Actuation of the firsttrigger 90 at the same time as the second trigger 92 may send a resetsignal to the controller 146 to zero a depth measurement (e.g., toestablish a reference point). Actuation of the first trigger 90simultaneously with the second trigger 92 may also sequence thecontroller 146 (e.g., to indicate a new task or tool portion 62 is to beutilized). The controller 146 may also display 5 administrative data 168(e.g., regarding an operation, patient, instrument status information,etc.).

In relation to the mode selection 150, the controller 146 may beconfigured to perform in various different modes using the modeselection 150. As an example, the different modes of operation maycorrespond with different relative placements of the leading edge 10 aof the tool portion 62 relative to the anatomy of a patient. Differentplacements of an orthopedic implant are depicted in FIGS. 6, 7, 8, and9. For instance, a bicortical bone cross-section such as those depictedin FIGS. 6-9 may include a hard outer cortex that surrounds a medullarylayer 102. In this regard, in bicortical operation is depicted in FIG.6, the leading edge 10 a of the tool portion 62 may be advanced througha first portion of the hard outer cortex 100 a, the medullary layer 102,and a second portion of the hard outer cortex 100 b. In turn, when theleading edge 10 a breaches the exterior of the second portion of thehard outer cortex 100 b, the instrument 100 may be arrested such thatthe tool portion 62 is placed as depicted in FIG. 6 where the leadingedge 10 a just breaches the entire bicortical length of the bone.Bicortical operation of the instrument 10 is generally described in U.S.Pat. No. 6,665,948 which is incorporated by reference herein.

FIG. 7 depicts another mode of operation corresponding to subchondralplacement of the tool portion 62. In this regard, the leading edge 10 aof the tool portion 62 is advanced through the first portion of hardouter cortex 100 a, the medullary layer 102, and a portion of the secondportion of hard outer cortex 100 b. In this regard, the instrument 10may be arrested when the leading edge 10 a is embedded in the secondportion of hard outer cortex 100 b as shown in FIG. 7.

FIG. 8 depicts another mode of operation corresponding to an endostealplacement of the tool portion 62. In this regard, the leading edge 10 amay be advanced through the first portion of hard outer cortex 100 a andthrough the medullary layer 102. The instrument 10 may be arrested whenthe leading edge 10 a reaches the second portion of hard outer cortex100 b such that the leading edge 10 a is disposed at the interface ofthe medullary layer 102 and the second portion of hard outer cortex 100b.

FIG. 9 depicts another mode of operation corresponding to multi-corticalplacement of the tool portion 62. In this mode, the leading edge 10 a ofthe tool portion 62 is advanced through a plurality of bones 101. Inthis regard, the number of bones through which the tool portion 62 is tobe advanced may be set such that instrument 10 is arrested when theleading edge 10 a of the tool portion 62 breaches the second portion ofhard outer cortex 100 b of the last bone 101 through which the toolportion 62 is to be advanced. Multi-cortical placement of the implant 62may involve setting occurrence flags that may at least in part be basedon the number of bones though which the tool portion 62 is to pass. Forinstance, if two bones are to be drilled through, the fourth occurrenceof the passing of the leading edge 10 a from a first medium into asecond medium having a lower density may indicate completion of theoperation. Also, while a bicortical placement is shown in FIG. 9, themulti-cortical mode may have submodes that allow for bicortical,subchondral, or endosteal placement through multiple bones usingidentification techniques to place the tool portion 62 in the last bonein the series of bones through which the tool portion 62 is to beadvanced. That is, the measurement system 40 may monitor penetrationthrough n−1 bones where n is the number of the last bone in which thetool portion 62 is to be placed. For the nth bone, any of the followingspecific techniques may be used for bicortical, subchondral, orendosteal placement of the tool portion 62 in the last bone.

Any of the foregoing placements may correspond with modes of operationof the instrument 10. For instance, selection of a mode corresponding toany one of the foregoing placements may be utilized by selection via themode selection 150 of the controller 146. As such, when a correspondingone of the modes is selected, the controller 146 may be operative tocontrol operation of the measurement system 40 so as to arrest theinstrument 10 when the leading edge 10 a of the tool portion 62 reachesthe placement designated for the mode or may output an alarm or takesome other action. In this regard, any one of a variety of approachesmay be utilized to determine when the tool portion 62 reaches thevarious placements described above. In this regard, various embodimentsof methods are described herein.

For instance, determination of the position of the leading edge 10 a ofthe tool portion 62 relative to the structure of a bone 101 may bedetermined by analyzing a signal output from a force sensor 50 and/ordisplacement sensor 42 of a measuring system 40 as described in the '948Patent incorporated by reference in its entirety above. While a forcesensor 50 is described herein, it may be appreciated that other tooldrive parameters may be monitored using an appropriate sensor asdescribed above. Thus, while a force sensor 50 is described, this is forillustrative purposes and is not limiting.

As the leading edge 10 a passes through the various interfaces of thebone structure 101, these interfaces may be detected based on signalsfrom the force sensor 50 and displacement sensor 42. For instance, whenthe leading edge 10 a passes from the first portion of hard cortex 100 ato the medullary layer 102, the tool portion 62 may experience a changein force (e.g., a decrease in the force) sensed by the force sensor 50and an increase in acceleration. The decrease in the force may bedetermined by taking the derivative of the signal output from the forcesensor 50. Specifically, the derivative of the signal output from theforce sensor 50 may become negative, indicating a negative rate ofchange of the force applied. Alternatively, a local minimum of a secondderivative of the force may be determined that corresponds to areduction in the force acting on the tool portion 62. For instance, asecond derivative of the force signal may be taken and the local minimumof the second derivative of the force signal may be determined using anyappropriate computational approach to determine such a state in theforce signal. Additionally, taking the second derivative of the outputfrom the displacement sensor 42 may provide a signal indicative of theacceleration. This technique may also be used to determine when the toolportion 62 passes through the second portion 100 b of hard cortex 100.This may be the first occurrence of a decrease in force and increase inacceleration in the case of unicortical operation or the secondoccurrence in the case of bicortical operation. In any regard, it may beappreciated that the change in the force may be used to detect when thetool portion 62 passes from one medium to another, whether it be anincrease or a decrease in force.

Moreover, it may be determined when the leading edge 10 a contacts thesecond portion 100 b of cortex 100 after passing through the medullarylayer 102. In this regard, a decrease in acceleration and an increase inforce as measured from the displacement sensor 42 and the force sensor50 may be utilized to determine the second portion 100 b of cortex 100has been contacted for endosteal placement. For subchondral placement, agiven displacement offset from the contacting of the second portion 100b of the cortex 100 may be used to advance the leading edge 10 a of thetool portion 62 partially into the second portion 100 b of cortex 100.

Such a context is depicted in FIGS. 11 and 12. FIG. 11 depicts a plot800 of various sensor outputs and/or calculated signals during a normalbicortical pass of a leading edge 10 a of a tool portion 62 through abone 101 of a patient. The plot 800 includes a displacement signal 802.The displacement signal 802 may be a directly measured signal from adisplacement sensor 42 of a measurement system 40. Alternatively, thedisplacement signal 802 may be derived from another sensor (e.g., as asecond integral of a signal from an accelerometer or the like). The plot800 also includes a velocity signal 804, which may be measured directlyor derived from a displacement sensor or an accelerometer. The plot 800also includes an acceleration signal 806. The acceleration signal 806may be measured (e.g., using an accelerometer or the like) or may bederived from the displacement signal 802 (e.g., as a second derivativeof the displacement signal 802). As discussed above, the velocity signal804 may be derived from either the displacement signal 802 (e.g., as afirst derivative thereof) or from the acceleration signal 806 (e.g., asa first integral thereof). Moreover, FIG. 11 may include a force signal808 representative of a change in force as measured by a force sensor50. In this regard, the force signal 808 may not depict an actual forcemeasure, but rather a first derivative of actual force. FIG. 12 shows anenlarged portion of the plot 800 in a region of interest around theinterfaces of the cortices.

As best seen in FIG. 12, the contact between the leading edge 10 a andinterface of the medullary layer 102 and the second portion 100 b ofcortex 100 occurs between 3.05 seconds and 3.1 second in the plot 800 atthe interface 801. This interface 801 coincides with the point at whichthe force signal 808 (representing the first derivative of the measuredforce) experiences a maximum (as may be measured by determining when asecond derivative of the measured force is positive). The interface 801may also coincide with a reduction in the acceleration signal 806. Assuch, when the force signal 808 is at a local maximum that coincideswith the acceleration being negative, the interface 801 may bedetermined.

However, while the foregoing approaches may assist in determiningplacement of a tool portion 62 in an idealized environment, it isrecognized that complications inherent to practical applications of themeasurement system 40 may result in false changes in signals beingdetected. This may lead to false positives in relation not detection ofthe position of the working tool 62. That is, the foregoing plots shownin FIGS. 11 and 12 may correspond to idealized systems in which therespective signal outputs analyzed are relatively free from noise andother signal artifacts. FIG. 13, in contrast, includes a plot 1300 thatis representative of a tool drive signal 1350 that represents an outputof a force sensor 50 as a tool portion 62 is advanced relative to a bone101. In FIG. 13, the plot 1300 is arranged relative to a representationof a bone 101 such that the distance axis 1302 corresponds to therelative structure shown in the bone 101 positioned below the plot 1300.The tool drive signal 1350 of the force sensor 50 is representedrelative to a force axis 1304.

The tool drive signal 1350 may have a first portion 1306 thatcorresponds to the tool portion 62 passing through the first portion ofthe hard outer cortex 100 a. The tool drive signal 1350 may have asecond portion 1308 corresponding to the tool portion 62 passing throughthe medullary layer 102 of the bone 101. The tool drive signal 1350 mayhave a third portion 1310 corresponding to the tool portion 62 passingthrough the second portion of the hard outer cortex 100 b. As may beappreciated, the first portion 1306 and third portion 1310 of the signalmay include a sharp increase in the measured force as represented in thetool drive signal 1350 resulting from the tool portion 62 passingthrough the relatively dense and hard outer cortex 100. The secondportion 1308 may result in a lower force that is relatively constant asthe tool portion 62 passes through the medullary layer 102.

While the tool drive signal 1350 is shown as corresponding to a forcesensor in FIG. 13, it may be appreciated that in various other contexts,alternative sensors may be used to measure and output tool drive signalscorresponding to alternative tool drive parameters for use indetermining placement of the leading edge 10 a of the tool portion 62.For instance, the measured tool drive parameter and corresponding tooldrive signal may include torque, an electrical characteristic of thedrive system 30 (e.g., resistance or the like), or other parameters thatare characteristic of the advancement of the tool portion 62 relative tothe anatomy of a patient. In the regard, appropriate sensors may beprovided including torque sensors, resistance detection sensors, or thelike.

In many contexts, such tool drive signals will be subjected to noise orother variations from a variety of sources as described above. Forinstance, certain surgeons may advance a tool portion 62 in a mannerthat may result in false positive detection of characteristicsassociated with placement of a tool portion 62. As described above, thismay include “pecking” the tool portion 62 with short, rapid advancementsrelative to the anatomy of the patient. Further still, the anatomyitself may present difficulties. For instance, a medullary layer 102 ofa bone may not be uniform. Rather, as shown in FIG. 13, the medullarylayer 102 may include trabeculae 104. Trabeculae 104 include a networkof osseous tissue that may be present in the medullary layer 102.

In any regard, the resulting tool drive signal 1350 may have localizedpeaks 1312 in the signal. As may be appreciated, when monitoring for anincrease in the tool drive signal 1350, such localized peaks 1312 may bedetected and result in false detections of either positive or negativechanges in the tool drive signal. As described above, the localizedpeaks 1312 may be a result of either the anatomy of the patient (e.g.,resulting from encountering trabeculae 104) or the manner in which thetool portion 62 is advanced. In any regard, the localized peaks 1312 mayrepresent a relatively brief (e.g., with respect to displacement 1302 ortime) increase in the tool drive signal 1350. As such, these localizedpeaks 1312 are preferably disregarded when analyzing the tool drivesignal 1350 in relation to any of the placement techniques describedabove in relation to FIGS. 6-9.

Accordingly, the controller 146 may monitor the drive output signal 1350to determine a change in the tool drive parameter (e.g., force) asrepresented in the tool drive signal 1350 relative to a given amount ofaxial displacement 1314 of the tool 62. Note that while a given amountof axial displacement 1314 is represented in FIG. 13 as an example ofone such given displacement 1314, FIG. 13 is not to scale and the actualrelation of the given displacement 1314 relative to the signal 1350 isnot represented. The identification of a change in the tool drive signal1350 relative to the given displacement 1314 may be accomplished by anumber of different potential approaches.

For instance, the controller 146 may apply a filter to the signal 1350with a smoothing factor that results in any localized peaks 1312 beingreduced or eliminated. As an example, the filter may comprise a low passfilter with a cutoff frequency tuned to disregard fast changingfrequencies in the signal. Moreover, the signal 1350 may be filteredrelative to the axial displacement of the tool portion 62 rather thantime, such that the cutoff frequency corresponds to changes in thesignal 1350 that only occur over relatively short axial displacementsuch as less than the given displacement 1314. Accordingly and as may beappreciated, the smoothing factor may be related to the givendisplacement 1314. Moreover, the given displacement 1314 may be selectedor determined based on a characteristic of a tool portion 62 and/oroperation performed utilizing the tool portion 62. In any regard,changes in the signal 1350 that occur only over distances less than thegiven displacement 1314 may be filtered or disregarded in relation tothe signal analysis used to determine placement of the tool portion 62.

Another approach is described in relation to FIGS. 15 and 16. Thisapproach may include integrating a tool drive signal 1506 to identify achange in the signal as described above. That is, this approach may beused in connection with any of the placement modes described above inrelation to FIGS. 6-9. That is, where a change in the tool driveparameter 1506 is to be monitored (e.g., for an increase or a decrease),the following approach may be utilized to detect such a change in thetool drive parameter 1506. As may be appreciated, this approach mayanalyze the tool drive parameter 1506 in relation to axial displacementrather than time such that the analysis is not dependent on or performedin relation to time.

A method 1400 for identifying a change in the tool drive parameter 1506is shown in FIG. 15 and will be described in relation to FIG. 16 thatincludes a plot 1500 of the tool drive parameter 1506. The plot 1500includes a vertical axis 1502 representative of the drive parametervalue and a horizontal axis 1504 representative of axial displacement ofthe tool portion 62. As can be appreciated, the tool drive parameter1506 may comprise a signal having noise that experiences variations thatmay not be attributable to the tool portion 62 passing between mediums.

In turn, the method 1550 may include defining 1552 an incremental axialdisplacement distance 1510. The incremental axial displacement distance1510 may correspond to the given amount of axial displacement referencedabove. The method 1550 may also include defining 1554 an integrationwindow 1508. The integration window may comprise a plurality ofincremental axial displacement distances 1510 to define the magnitude ofthe integration window 1508. For instance, in FIG. 16, five incrementalaxial displacement distances 1510 may comprise an integration window1508, however other numbers of incremental axial displacement distances1510 may be chosen to comprise the integration window 1508 withoutlimitation. As can also be appreciated in FIG. 16, a plurality ofintegration windows 1508 a, 1508 b, 1508 c, . . . 1508 n may be defined.In turn, the method 1550 may include obtaining 1556 the tool driveparameter 1506 (e.g., as a signal output from a sensor on the instrument10).

The method 1550 may include integrating 1558 the tool drive parameter1506 over a first integration window 1508 a to generate an integratedtool drive parameter. The integrated tool drive parameter may comprisethe summed value of the tool drive parameter 1506 over the integrationwindow 1508. This may represent the area under the curve representativeof the tool drive parameter 1506 shown in FIG. 16. For instance, in FIG.16, as the tool drive parameter 1506 is obtained for the firstintegration window 1508 a, the integral of the tool drive parameter 1506may be determined by summing the tool drive parameter 1506 over each ofthe incremental axial displacement distances 1510 in the firstintegration window 1508 a.

The method 1550 may also include comparing 1560 the integrated tooldrive parameter to an integral threshold. If the integrated tool driveparameter does not exceed the integral threshold, the method 1550 mayinclude advancing 1564 the tool portion by an incremental axialdisplacement distance 1510 and obtaining 1556 additional tool driveparameter 1506 data. For instance, if the integrated tool driveparameter does not exceed the integral threshold within integrationwindow 1508 a, the tool may be advanced 1564 by an incremental axialdisplacement distance 1510 to define a new integration window 1508 b. Asmay be appreciated, while additional tool drive parameter 1506 data isshown distal to the first integration window 1508 a relative to theaxial displacement 1504, when collecting in real time, the firstintegration window 1508 a may correspond to the most recent tool driveparameter 1506 data collected. As such, tool drive parameter data 1506may be collected as the integration window 1508 is advanced such thatthe current integration window 1508 may represent the most distalportion of the tool drive parameter 1506 data. Accordingly, integrationwindows 1508 a, 1508 b, and 1508 c represent historical windows in FIG.16 for purposes of illustration.

This process may repeat at 1508 c and so forth. However, returning tothe comparing 1560, if the integrated tool drive parameter exceeds theintegral threshold, then the method 1550 may include identifying 1562 achange in the tool drive parameter 1506. This identification 1562 of thechange in the tool drive parameter 1506 may be used in conjunction withany process for determining the tool portion 62 passing from one mediumto another medium. Such an identification 1562 may occur as shown inFIG. 16 at 1508 n, which is the nth integration window in which theintegrated tool drive parameter for the integration window 1508 nexceeds the integration threshold based on the increase in the tooldrive parameter 1506. As can be appreciated, the tool drive parameter1506 also experienced an increase in the integration windows 1508 a,1508 b, and 1508 c. However, this increase was not significant over thetotality of each of the integration windows to exceed the integrationthreshold. This demonstrates this approach's ability to filter outchanges in the tool drive parameter 1506 that are not significant eventsto avoid false detection.

Additionally or alternatively, the controller 146 may be operative tocalculate a moving average of the signal 1350 relative to the axialdisplacement measure 1302. That is, the moving average may be calculatedby averaging values of the signal 1350 over the given displacement 1314.In turn, a change in the tool drive parameter may be identified fordetermination or identification of tool portion 62 placement in responseto identification of an inflection of the moving average (e.g.,including when the derivative of the moving average moves from positiveto negative or negative to positive depending on the context). As willbe appreciated in the discussion to follow, the moving average may becalculated for the tool drive parameter relative to axial displacementrather than relative to time. In this regard, the tool drive parametermay be analyzed without respect to time as the moving average may becalculated relative to axial displacement.

For instance, when the tool portion 62 moves from a medullary layer 102of the bone 101 to a cortex layer 100 of the bone 101, the movingaverage may experience an inflection corresponding to a minimum in themoving average. Alternatively, when the tool portion 62 moves from acortex layer 100 of the bone 101 to a medullary layer 102 of the bone101, the moving average may experience an inflection corresponding to amaximum in the moving average.

It may be appreciated that the given distance 1314 over which a changein the signal 1350 must occur to be recognized in relation to theanalysis of the signal 1350 for determining placement of the toolportion 1314 may vary based on the context. However, in at least someembodiments, the given distance 1314 may be at least about 0.5 mm. Inother embodiments, the given distance 1314 may preferably be about 1.0mm. In further embodiments, the given distance 1314 may be at leastabout 1.5 mm, 2.0 mm, 2.5 mm, or even 3 mm.

Still a further approach that may employ moving averages is described inrelation to FIGS. 17 and 18. FIG. 17 depicts a method 1600 that mayutilize the calculation of two moving averages and comparison of themoving averages relative to one another. FIG. 18 depicts a plot 1700showing various signals that may be used in the method 1600. Thevertical axis 1702 of the plot 1700 may represent a value of variousparameters monitored or calculated in the method 1600. The horizontalaxis 1704 may correspond to the axial displacement of the tool portion62. Like the moving average approach described above, the two movingaverages may be calculated relative to axial displacement rather thantime such that the tool drive parameter may be monitored without regardto time.

The method 1600 may begin by obtaining 1602 a tool drive parameter 1706.As can be appreciated from the plot 1700, the tool drive parameter 1706may include some noise in the signal. As such, the method 1600 mayinclude calculating 1604 a short term moving average 1708. In addition,the method 1600 may include calculating 1606 a long term moving average1710. The short term moving average 1708 may be calculated 1604 usingtool drive parameter values over a first increment (e.g., related to afirst axial displacement of the leading edge of the tool portion) thatis smaller than a second increment (e.g., related to a second axialdisplacement of the leading edge of the tool portion) over which thelong term moving average 1710 is calculated 1606. As described above,the increment over which the moving averages are calculated may be withrespect to axial displacement such that sampled values of the tool driveparameter 1706 over each respective increment of axial displacement isused to calculate the respective average. Alternatively, the incrementmay be relative to time. In either regard, the long term moving average1710 may include more values of the tool drive parameter 1706 than theshort term moving average 1708. In this regard, the short term movingaverage 1708 may capture more rapid changes in the tool drive parameter1706 while the long term moving average 1710 may reflect only changes inthe tool drive parameter 1706 that occur over a longer axialdisplacement.

As such, the method 1600 may include comparing 1608 the short termmoving average 1708 to the long term moving average 1710. As can beappreciated in the plot 1700, as the leading edge 10 a of the toolportion 62 transitions form one medium to another, the tool driveparameter 1706 may rise (e.g., the force on the tool portion 62 mayincrease). As shown in the plot 1700, the short term moving average 1708may relatively closely track the increase in the tool drive parameter1706, while the long term moving average 1710 may lag the tool driveparameter 1706. Accordingly, at the comparing 1610, if the short termmoving average 1708 differs from the long term moving average 1710 bygreater than a differential threshold, the method 1600 may progress asdescribed in greater detail below. If the differential threshold is notexceeded, the method 1600 may turn to obtaining 1602 the tool driveparameter 1706. For instance, as can be seen in FIG. 18, there is ashort term rise 1718 in the tool drive parameter 1706 prior to theidentified change 1716. In this area, while the short term movingaverage 1708 may deviate from the long term moving average 1710, thedifferential did not exceed the differential threshold such that nochange was identified. However, at 1716, the differential exceeded thedifferential threshold, thus indicating the change 1718.

The method 1600 may also include other checks to ensure that anidentified change in the tool drive parameter 1706. For instance, themethod 1600 may also include checking 1612 an acceleration signal 1714.The displacement sensor 42 may allow for a calculation of a velocitysignal 1712 (e.g., by calculating a first derivative of thedisplacement). The velocity signal 1712 may be sampled at a given amountof axial displacement to determine if the tool portion is accelerating(velocity is increasing) or decelerating (velocity is decreasing). Thisacceleration indication may be determined by taking the derivative ofthe velocity signal 1712. The acceleration signal 1714 may indicate howmany consecutive samples in which the tool portion 62 has decelerated.The consecutive samples may comprise an average of the acceleration overa given axial displacement. The check 1612 may include determining thata threshold number of samples in which there is deceleration occursprior to determining a change. For instance, in the plotted example,that threshold number of deceleration samples may be three. As such, theacceleration signal 1714 may be at an initial value of three and reducedby one each time a sample is taken in which a declaration is detectedfrom the velocity signal 1714. If the tool portion 62 accelerates (e.g.,undergoes positive acceleration rather than negative accelerationreferred to herein as deceleration) at any sample, the value of theacceleration signal 1714 may be reset to the initial value. Accordingly,as can be appreciated at the detected change 1716, both the differentialthreshold may be exceeded and the deceleration value may be 0,indicative of three consecutive samples in which the tool portion 62 hasdecelerated. In contrast, even in the short term rise 1718 area of theplot 1700, if the differential threshold had been exceeded, a changewould not have been detected because check 1612 would have indicatedthat the acceleration signal 1714 had not had a sufficient number ofconsecutive instances of deceleration.

The method 1600 may also include checking 1614 a number of toolparameters. These tool parameters may include determinations that theinstrument is active (e.g., the trigger for advancing the instrument isdepressed and the motor of the instrument is running) upon occurrence ofthe identification of the differential in the moving average exceedingthe differential threshold. The tool parameters observed in the checking1614 may also include determining if the drill is “zeroed” or reset whenthe leading edge 10 a of the working portion 62 is coplanar with areference surface of a displacement sensing arm. This checking 1614 mayalso include observing the one or more sensors of the instrument 100 todetermine if the sensor outputs are in a given acceptable range (e.g.,prior to operation or during operation). The method 1600 may alsoinclude checking 1616 that the axial displacement of the tool portion 62is greater than the previous max displacement at the occurrence of thechange. For instance, if the tool portion 62 had been retracted andadvanced again and the detection of the change occurred in a location ofthe axial displacement that was less than the maximum displacement(e.g., in a region in which the tool is readvanced) the change may beignored and the method 1600 may continue to obtain 1602 the tool driveparameter. However, if all of the foregoing additional checks aresatisfied, then the method 1600 may include identifying 1618 a change inthe tool drive parameter.

With further reference to FIG. 14, a flowchart is shown depicting anembodiment of a method 1400 in which the instrument 10 described abovemay be utilized. The method 1400 may include placing 1402 the instrument10 relative to the anatomy of the patient to be operated upon. Once theinstrument 10 has been placed 1402, the displacement sensor 42 of theinstrument 10 may be zeroed (e.g., through interaction with thecontroller 146). Thereafter, the method 1400 may include advancing 1404the instrument 10, specifically the tool portion 62, relative to theanatomy of the patient. In this regard, a user may initiate operation ofthe instrument 10 (e.g., by selecting the appropriate trigger 90/92)advancing the leading edge 10 a of the tool portion 62.

The method 1400 may further include monitoring 1406 the displacementsensor 42. The monitoring 1406 may include communicating an output ofthe displacement sensor 42 to the controller 146. The method 1400 mayalso include monitoring 1408 the force sensor 50 in relation to a givenamount of displacement 1314. As described above, any or all of theapproaches to monitoring 1408 the force sensor in relation to a givenamount displacement 1314 may be utilized. Accordingly, the method 1400may include determining 1409 placement of the tool portion based on thedisplacement signal and the force signal as analyzed relative to thedisplacement. If the selected placement is not identified, the method1400 may iterate such that the instrument 10 is continued to be advanced1404. However, if the selected placement is achieved, the method mayinclude ceasing 1410 operation of the instrument 10. Additionally oralternatively, the method 1400 may include outputting 1412 one or morealerts and/or measuring the travel of the tool portion 62 upon theselected placement being achieved. By the selected placement, it ismeant the designated placement of the tool portion 62 based on thespecific characteristics of the displacement sensor 42 and force sensor50 in relation to a given amount displacement for a given mode asidentified based on the mode that has been selected at the controller146.

Accordingly, the foregoing disclosure includes details regarding systemsand methods that may be used for improved placement of a tool portion 62of a powered instrument 10. Specifically, the foregoing approachesprovide the ability to accurately place the tool portion 62 relative tospecific portion of anatomy of the patient as selected by the userselection of a mode at the controller 146. The placement mayspecifically be determined based on analysis of a tool drive signal 1350relative to a given amount of axial displacement of the leading edge 10a of the tool 62 such that noise and/or other artifacts in the tooldrive signal 1350 may be disregarded to avoid false indications ofplacement resulting from such noise and/or other artifacts. In turn,more accurate, reliable, and/or repeatable operation of the instrument10 may be provided.

While the invention has been illustrated and described in detail in thedrawings and foregoing description, such illustration and description isto be considered as exemplary and not restrictive in character. Forexample, certain embodiments described hereinabove may be combinablewith other described embodiments and/or arranged in other ways (e.g.,process elements may be performed in other sequences). Accordingly, itshould be understood that only the preferred embodiment and variantsthereof have been shown and described and that all changes andmodifications that come within the spirit of the invention are desiredto be protected.

1. A measurement system for use with a powered surgical instrument forsensing a position of a leading edge of a tool portion relative toanatomic structures of a patient, the measurement system comprising: afirst sensor disposed with respect to the powered surgical instrument tomeasure a tool drive parameter that is characteristic of the toolportion acting on the patient and output a tool drive signalrepresentative the tool drive parameter as the tool portion is advancedrelative to anatomy of the patient; a displacement sensor disposed withrespect to the powered surgical instrument to measure an axialdisplacement of the leading edge of the tool portion relative to areference point and output a displacement signal representative of theaxial displacement; and a controller in operative communication with thefirst sensor to receive the tool drive signal and in operativecommunication with the displacement sensor to receive the displacementsignal, wherein the controller is operative to identify a change in thetool drive parameter over a given amount of axial displacement of theleading edge of the tool portion that is indicative of the leading edgeof the tool portion moving through an interface between anatomicstructures of the patient, wherein the controller is operative todetermine a moving average for the tool drive parameter with respect tothe axial displacement of the leading edge of the tool portion relativeto the anatomy of the patient.
 2. The measurement system of claim 1,wherein the given amount of axial displacement of the leading edge ofthe tool portion is at least about 0.1 mm.
 3. The measurement system ofclaim 1, wherein the controller is in control of the operation of adrive motor of the powered surgical instrument and is operative to stopthe drive motor in response to identifying the interface betweenanatomic structures of the patient.
 4. The measurement system of claim1, wherein the tool drive parameter comprises one of an axial forceacting on the tool portion, a torque acting on the tool portion, or anelectrical characteristic of a drive motor of the powered surgicalinstrument.
 5. The measurement system of claim 1, wherein the anatomicstructures of the patient have different densities. 6.-7. (canceled) 8.The measurement system of claim 1, wherein the controller is operativeto identify the change in the tool drive parameter relative to a givenamount of axial displacement of the leading edge of the tool portionbased on an inflection of the moving average.
 9. The measurement systemof claim 8, wherein the interface is from a medullary layer of a bone toa cortex layer of the bone, and wherein the moving average comprises aninflection from a minimum of the moving average over the given amount ofaxial displacement of the leading edge of the tool portion.
 10. Themeasurement system of claim 8, wherein the interface is from a cortexlayer of a bone to an exterior of the bone, and wherein the movingaverage comprises an inflection from a maximum of the moving averageover the given amount of axial displacement of the leading edge of thetool portion.
 11. The measurement system of claim 1, wherein theinterface through which the leading edge of the tool moves is from amedullary layer of a bone to a cortex layer of the bone. 12.-15.(canceled)
 16. The measurement system of claim 11, wherein thecontroller is further operative to: generate a short term moving averagefor the tool drive parameter with respect to a first axial displacementof the leading edge of the tool portion relative to the anatomy of thepatient; generate a long term moving average for the tool driveparameter with respect to a second axial displacement of the leadingedge of the tool portion relative to the anatomy of the patient, whereinthe second axial displacement is greater than the first axialdisplacement; and identify the change in the tool drive parameter whenthe short term moving average diverges from the long term moving averageby at least a differential threshold.
 17. The measurement system ofclaim 16, wherein the controller is operative to monitor for the changein the tool drive parameter when the leading edge of the tool portiondecelerates in three consecutive instances of the given amount of axialdisplacement of the leading edge of the tool portion.
 18. Themeasurement system of claim 17, wherein the controller is operative todetermine the deceleration in the leading edge based on the displacementsignal by calculating the second derivative of the displacement signal.19. A method for use with a powered surgical instrument for sensing aposition of a leading edge of a tool portion relative to anatomicstructures of a patient, the method comprising: measuring a tool driveparameter that is characteristic of the tool portion acting on thepatient as the tool portion is advanced relative to anatomicalstructures of the patient at a first sensor of the powered surgicalinstrument; outputting a tool drive signal representative of the tooldrive parameter; measuring at a displacement sensor of the poweredsurgical instrument an axial displacement of the leading edge of thetool portion relative to a reference point; outputting a displacementsignal representative of the axial displacement; monitoring the tooldrive signal and the displacement signal as the leading edge of the toolportion is advanced relative to the anatomical structures of thepatient; and identifying a change in the tool drive parameter over agiven amount of axial displacement of the leading edge of the toolportion that is indicative of the leading edge of the tool portionmoving through an interface between anatomic structures of the patient;and determining a moving average of the tool drive parameter withrespect to the axial displacement of the leading edge of the toolportion relative to the anatomical structures of the patient.
 20. Themethod of claim 19, wherein the given amount of axial displacement ofthe leading edge of the tool portion is at least about 0.1 mm.
 21. Themethod of claim 19, further comprising: stopping operation of a drivemotor of the powered surgical instrument in response to the identifying.22. The method of claim 19, wherein the tool drive parameter comprisesone of an axial force acting on the tool portion, a torque acting on thetool portion, or an electrical characteristic of a drive motor of thepowered surgical instrument.
 23. The method of claim 19, wherein theanatomic structures of the patient have different densities. 24.-25.(canceled)
 26. The method of claim 19, wherein the identifying furthercomprises identifying an inflection in the moving average.
 27. Themethod of claim 26, wherein the interface is from a medullary layer of abone to a cortex layer of the bone, and wherein the moving averagecomprises an inflection from a minimum of the moving average over thegiven amount of axial displacement of the leading edge of the toolportion.
 28. The method of claim 26, wherein the interface is from acortex layer of a bone to an exterior of the bone, and wherein themoving average comprises an inflection from a maximum of the movingaverage over the given amount of axial displacement of the leading edgeof the tool portion.
 29. The method of claim 19, wherein the interfacethrough which the leading edge of the tool moves is from a medullarylayer of a bone to a cortex layer of the bone. 30.-32. (canceled) 33.The method of claim 29, further comprising: generating a short termmoving average for the tool drive parameter with respect to a firstaxial displacement of the leading edge of the tool portion relative tothe anatomy of the patient; generating a long term moving average forthe tool drive parameter with respect to a second axial displacement ofthe leading edge of the tool portion relative to the anatomy of thepatient, wherein the second axial displacement is greater than the firstaxial displacement; and identifying the change in the tool driveparameter when the short term moving average diverges from the long termmoving average by at least a differential threshold.
 34. The method ofclaim 33, further comprising: monitoring for the change in the tooldrive parameter when the leading edge of the tool portion decelerates inthree consecutive instances of the given amount of axial displacement ofthe leading edge of the tool portion.
 35. The method of claim 34,further comprising: determining the deceleration in the leading edgebased on the displacement signal by calculating the second derivative ofthe displacement signal.
 36. A measurement system for use with a poweredsurgical instrument for sensing a position of a leading edge of a toolportion relative to anatomic structures of a patient, the measurementsystem comprising: a first sensor disposed with respect to the poweredsurgical instrument to measure a tool drive parameter that ischaracteristic of the tool portion acting on the patient and output atool drive signal representative the tool drive parameter as the toolportion is advanced relative to anatomy of the patient; a displacementsensor disposed with respect to the powered surgical instrument tomeasure an axial displacement of the leading edge of the tool portionrelative to a reference point and output a displacement signalrepresentative of the axial displacement; and a controller in operativecommunication with the first sensor to receive the tool drive signal andin operative communication with the displacement sensor to receive thedisplacement signal, wherein the controller is operative to identify achange in the tool drive parameter over a given amount of axialdisplacement of the leading edge of the tool portion that is indicativeof the leading edge of the tool portion moving through an interfacebetween anatomic structures of the patient, wherein the controller isoperative to filter the tool drive signal relative to the given amountof axial displacement of the leading edge of the tool portion such thatchanges in the tool drive parameter over distances less than the givenamount of axial displacement are not identified as indicative of theleading edge of the tool portion moving through the interface betweenanatomic structures of the patient.
 37. The measurement system of claim36, wherein the given amount of axial displacement of the leading edgeof the tool portion is at least about 0.1 mm.
 38. The measurement systemof claim 36, wherein the controller is in control of the operation of adrive motor of the powered surgical instrument and is operative to stopthe drive motor in response to identifying the interface betweenanatomic structures of the patient.
 39. The measurement system of claim36, wherein the tool drive parameter comprises one of an axial forceacting on the tool portion, a torque acting on the tool portion, or anelectrical characteristic of a drive motor of the powered surgicalinstrument.
 40. The measurement system of claim 36, wherein the anatomicstructures of the patient have different densities.
 41. A method for usewith a powered surgical instrument for sensing a position of a leadingedge of a tool portion relative to anatomic structures of a patient, themethod comprising: measuring a tool drive parameter that ischaracteristic of the tool portion acting on the patient as the toolportion is advanced relative to anatomical structures of the patient ata first sensor of the powered surgical instrument; outputting a tooldrive signal representative of the tool drive parameter; measuring at adisplacement sensor of the powered surgical instrument an axialdisplacement of the leading edge of the tool portion relative to areference point; outputting a displacement signal representative of theaxial displacement; monitoring the tool drive signal and thedisplacement signal as the leading edge of the tool portion is advancedrelative to the anatomical structures of the patient; identifying achange in the tool drive parameter over a given amount of axialdisplacement of the leading edge of the tool portion that is indicativeof the leading edge of the tool portion moving through an interfacebetween anatomic structures of the patient; and filtering the tool drivesignal relative to the given amount of axial displacement of the leadingedge of the tool portion such that changes in the tool drive parameterover distances less than the given amount of axial displacement are notidentified as indicative of the leading edge of the tool portion movingthrough the interface between anatomic structures of the patient. 42.The method of claim 41, wherein the given amount of axial displacementof the leading edge of the tool portion is at least about 0.1 mm. 43.The method of claim 41, further comprising: stopping operation of adrive motor of the powered surgical instrument in response to theidentifying.
 44. The method of claim 41, wherein the tool driveparameter comprises one of an axial force acting on the tool portion, atorque acting on the tool portion, or an electrical characteristic of adrive motor of the powered surgical instrument.
 45. The method of claim41, wherein the anatomic structures of the patient have differentdensities.